The longterm aim of the project outlined in this proposal is to understand how cells that originate from a seemingly similar precursor in the neural crest differentiate to produce the diverse cellular phenotypes present in the vertebrate nervous system. The avian embryo is one of the best known models to study the early steps in this differentiation process, in particular the transition of neural crest precursors to chromaffin cells or embryonic neurons. These embryonic cells are characterized by a high degree of plasticity and have been shown to respond to various growth factors with changes in the expression of morphological and/or biochemical properties. However, most of these studies have been limited in scope to a single growth factor, a single cell type or a single morphological or biochemical property. The main goals of this grant are to describe the effects of members of the neurotrophin family on the sympathoadrenal system and to determine the role of nonneuronal cells on the plasticity of neurons and chromaffin cells of this system. An extensive study on the effects of five neurotrophin members will be achieved by analyzing their effects on two cell types that originate from the same precursor, the sympathetic neurons and the adrenal chromaffin cells. The parameters to be analyzed are: one morphological parameter, neurite extension, and five biochemical parameters, the expression of the catecholamines, epinephrine and norepinephrine, and the neuropeptides, enkephalin, neuropeptide Y and somatostatin. The proposed experiments will serve to identify possible factors that are involved in the differentiation and acquisition of particular phenotypes. Results will lead to a better understanding of the processes of differentiation and plasticity in cells of the nervous and endocrine systems.